In general, in a hydraulic circuit of a working machine such as a construction machine, have various control valves to control actuations of various hydraulic actuators, such as hydraulic cylinders or hydraulic travel motors, and those control valves requires urgent maintenance actions such as repair or replacement, in case a failure has occurred. However, for example, in case a problem such as output shortage of a hydraulic actuator, insufficient hydraulic line pressure, or unstable pump pressure, has occurred to the hydraulic circuit, it may take a significant amount of time to determine which control valve component has caused the issue because there are multiple components to the control valve which can be the cause of the problem. Many troubleshooting and test operations may be required to resolve the hydraulic circuit problem which is typically resolved by replacing the control valve component which caused the problem. In particular, for construction machines, there has been known a control valve system with four of independent metering valves to control hydraulic oil flow from/to a hydraulic actuator, which has the first and the second meter-in valves that control hydraulic oil flow to a pair of the hydraulic actuator ports and the first and the second meter-out valves that control hydraulic oil flow from the pair of the hydraulic actuator ports, for the purpose of fine and efficient hydraulic actuator control with independent electronic control of each metering valve (see Patent Document 1, for example). Such a hydraulic circuit with independent metering valves has a complicated configuration because there are not only four metering valves per one hydraulic actuator, but more valves such as a combiner valve to combine multiple pump flows or relief valves to control pump pressure, which are for purposes outside of hydraulic actuator control. Therefore in case a problem occurred to the hydraulic circuit, it takes lots of time and requires higher level understanding of the hydraulic circuit configuration for a service engineer to determine the failed control valve component among lots of control valve components which can cause the problem.
On the other hand, as a control valve fault diagnostic system for hydraulic circuit of working machines, there has been known technology for a control device to output control signals to control valves, which has interchangeable 2 control modes, the first one is normal control mode for normal control procedures and the other one is fault diagnostic mode for particular fault diagnostic procedures. And in the fault diagnostic mode, a control valve fault is detected based on the hydraulic pump discharge pressure during the fault diagnostic procedure is applied to the control valve. (see Patent Document 2, for example).
Patent Document 1: Japanese Patent Application Laid-open No. 10-311301
Patent Document 2: Japanese Patent Application Laid-open No. 2000-46015